The role of synaptic vesicles in cholinergic transmission is being evaluated by correlated electron microscopic and electrophysiological methods. In the present work we are investigating the time-couse of development and recovery of previously described ultrastructural alterations of synapses in the cat superior cervical ganglia. Preganglionic sympathetic trunks are electrically stimulated at various frequencies and for various periods and nictitating membrane contractions are recorded. Animals are perfused intraaortically with an aldehyde fixative at the end of stimulation or after a period of recovery. Both stimulated and contralateral control ganglia are removed and studied. Synaptic vesicle content, plasma membrane surface area, lengths of axo-dendritic apposition, and presynaptic densities, coated vesicles and extravesicular membrane are being evaluated using quantitative electron microscopy. In other studies, the frog sympathetic ganglia in vitro are being used. Electrical stmulation and ganglionic transmission are monitored by recording postganglionic potentials. The ultrastructural effects of chemical stimulation with hypertonic Kion, or preganglionic electrical stimulation in the presence of DNP or low Ca ion and high Mg ions concentration are being evaluated. BIBLIOGRAPHIC REFERENCES: Pysh, J.J. and R.G. Wiley 1975 Evidence for transmitter secretion by exocytosis in the cat superior cervical ganglion. Proc. Tenth Intern. Congress Anatomists, Eichi Yamada, Editor; Science Council of Japan. Pysh, J.J. and R.G. Wiley 1975 Ultrastructura evidence for acetylcholine release by exocytosis in cat superior cervical ganglion, Report of Winter Conference on Brain Research, U.C.L.A. Brain Information Service (in press).